The present invention relates to a microwave oven for cooking and thawing foods by applying irradiation of the microwaves generated in a magnetron.
When the microwave oven is operated without a heat load such as food or the like to absorb microwaves, or only a very small load is placed therein, local temperatures rise, in other words, a hot spot is generated therein, posing the danger of cracking a turntable, melting a holder of the table, melting and making a hole in a wall of the cooking chamber, or causing a fire due to short wave leakage or overheating.
Therefore, up to the present, by providing a pseudo-load, generally called a dummy load, in a wave guide or on the turntable as a light load, above-mentioned accidents such as an abnormal concentration of the short waves around the turntable and the holder of the table, and the occurrence of a hot spot on the wall of the cooking chamber have been prevented by the use of a dummy load even if the oven is used in an unloaded condition.
However, in this conventional construction, as the magnetron is driven for long time in a condition equivalent to being unloaded even if operated under a light load, it is hard to prevent over-loading of the magnetron and a drop in the service life of the magnetron. Further, while operating the oven under a light load, as the microwaves are absorbed by the dummy load, a drop in heating efficiency is also inevitable.
The present invention solves these problems or drawbacks, and the object thereof is to provide a microwave oven able to prevent any hot spot occurrence and the destruction of the magnetron by stopping the flow of the short waves into the cooking chamber when there is no load.